In 1876 Reimer together with Tiemann was the first to isolate and identify hydroxyaldehydes as the principal reaction products of phenols and chloroform in an alkaline medium. The direct introduction of an aldehyde group into an aromatic nucleus occurred under the Reimer-Tiemann reaction conditions. Using varying molar ratios of alkali to phenol to which a molar excess of chloroform is added with vigorous stirring, at temperatures between 25.degree. C.-70.degree. C., the reaction is allowed to proceed for several hours or even days. The chemistry of the Reimer-Tiemann reaction has been summarized, for example, by Hans Wynberg, Chemical Reviews, Vol. 60, 169 (1960), and by Ferguson, Chemical Reviews, Vol. 38, 229 (1946). Aldehyde yields are obtained in the following ranges, 35-40 percent o-hydroxybenzaldehyde, 8-12 percent p-hydroxybenzaldehyde, based on chloroform.